1. Field of the Invention
The present invention generally relates to an external-control type fan clutch device that controls fan rotation for cooling engine in an automobile or the like according to a change in ambient temperature or a rotation change of an engine, and in particular, relates to an external-control type fan clutch device that can suppress unnecessary rotation of a cooling fan occurring when the cooling fan transitions from a stop state to a rotating state.
2. Description of the Related Art
Conventionally, as a fan clutch device of such a type, there has been known a viscous friction clutch for driving a cooling fan in a motor vehicle (see U.S. Pat. No. 7,886,886). The viscous friction clutch comprises a driving disk and a housing, an annular supply chamber and a working chamber, a supply device for supplying shear fluid (oil) from the supply chamber into the working chamber and a return device for returning the shear fluid from the working chamber to the supply chamber wherein part of the supply chamber includes a storage chamber for the shear fluid, the storage chamber being separated from the working chamber by a remainder of the supply chamber, and the viscous friction clutch has such a feature as the supply chamber being arranged in the driving disk; the storage chamber comprising an annular segment; the annular segment of the storage chamber being formed as a supplementary receptacle; or the supply chamber including at least one supply port and at least one return port (recovery port); the ports respectively forming part of the supply device and return device. An external-control type fan clutch device having such a configuration adopts such a system that an oil storage chamber is provided in an oil supply chamber, and unnecessary rotation of a cooling fan occurring when the cooling fan transitions from a stop state to a rotating state is suppressed by reducing an amount of oil leaking from an oil storage chamber side to a working chamber side through an oil supply port and an oil recovery port at the stop time of the cooling fan.
However, in the case of the above-described conventional external-control type fan clutch device, since oil can be stored in the oil storage chamber at the stop time of the cooling fan, a leaking amount of oil to the working chamber can be reduced, but an amount of oil which cannot be stored in the oil storage chamber at the stop time leaks from the oil recovery port and the oil supply port due to stopping positions of the oil supply port and the oil recovery port at the stop time of the cooling fan and thereby there has been such a drawback that a suppressing effect of the unnecessary rotation of the fan at a starting time of the engine cannot be obtained sufficiently.